JP5978760B2 - Exhaust gas purification method and apparatus for internal combustion engine - Google Patents

Description

  The present invention relates to an exhaust gas purification method and apparatus for an internal combustion engine.

  In vehicles, particularly automobiles, an increasing number of hybrid vehicles are equipped with an internal combustion engine, that is, an engine and a traveling motor. In a hybrid vehicle, electric power is generated by driving a generator by an engine, and the generated electric power is used for supplying power to a traveling motor and charging a battery.

  On the other hand, in order to improve fuel efficiency, the engine is operated leaner than the stoichiometric air-fuel ratio. Then, a NOx catalyst is disposed in the exhaust passage in order to reduce NOx discharged along with the lean operation. In Patent Document 1, in a hybrid vehicle, normally, lean operation is performed, and when the NOx occlusion amount in the NOx catalyst increases, the engine is operated at a rich air-fuel ratio to purge the stored NOx. Is disclosed. Patent Document 1 also discloses that the motor torque is controlled so that the total torque applied to the drive wheels does not change between the lean operation and the rich operation of the engine.

JP 2008-68802 A

  By the way, in the hybrid vehicle, when the lean operation of the engine that drives the generator is continued, the NOx occlusion amount in the NOx catalyst increases to the upper limit value. In this case, when the engine is switched to the rich operation to purge the stored NOx, it is impossible to efficiently purge the NOx unless the NOx catalyst reaches the activation temperature. For this reason, a temperature sensor for detecting the temperature of the NOx catalyst is separately provided, and the operation is switched to the rich operation on condition that the temperature of the NOx catalyst detected by the temperature sensor is equal to or higher than a predetermined temperature corresponding to the activation temperature. It is possible. However, in this case, a separate temperature sensor for detecting the temperature of the NOx catalyst is required.

  Further, from various viewpoints, the NOx purge is performed as frequently as possible, for example, when the NOx storage of the NOx catalyst is in a state where there is a margin, for example, when the storage amount becomes 50% or more, the rich operation is switched to perform the purge. Can be considered. In such a case, it often happens that the NOx catalyst does not reach the activation temperature.

  The present invention has been made in view of the above circumstances, and its purpose is to efficiently purge NOx by confirming that the NOx catalyst has reached the activation temperature without depending on the temperature sensor. An object of the present invention is to provide an exhaust gas purification method and apparatus for an internal combustion engine that can be used.

In order to achieve the object, the following solution is adopted in the method of the present invention. That is, as described in claim 1,
An engine in which an NOx catalyst is disposed in the exhaust passage, a generator driven by the engine, a battery storing electric power generated by the generator, a driving motor driven by the electric power generated by the generator, and the battery; An exhaust gas purification method for an internal combustion engine comprising:
A first step of detecting a storage amount of NOx in the NOx catalyst;
When the NOx occlusion amount detected in the first step is greater than or equal to a predetermined amount, the engine operating state is changed from a lean operating state at an air / fuel ratio leaner than the stoichiometric air / fuel ratio to a rich air / fuel ratio below the stoichiometric air / fuel ratio. A second step of switching to a rich operation state at a fuel ratio;
With
The switching to the rich operation state continues for a predetermined time or more set as a time sufficient for the temperature of the power generation in the lean operation state to be raised until the NOx catalyst reaches the activation temperature or higher. Allowed on the condition that
When the NOx occlusion amount detected in the first step is equal to or greater than the predetermined amount, when switching to the rich operation state is not permitted, the operation time in the rich operation state performed thereafter is extended,
The operation time in the rich operation state is an addition time obtained by adding the extension time to the basic time that is the minimum operation time,
The extended time is increased as the time during which switching to the rich operation state is not permitted is longer,
It is like that. According to the above solution, when the engine is switched to the rich operation state, the time during which the engine is performing lean operation while generating power in advance has been continuously performed for a predetermined time or more. Since the temperature reaches a sufficiently activated temperature, the NOx purge when the rich operation is performed can be efficiently performed. In addition, since the lean operation time during which power generation is performed is continuously performed for a predetermined time or more, it is determined whether the NOx catalyst is higher than the activation temperature. It is possible not to provide a sensor for detection.

Further, since the NOx catalyst is not activated and the rich operation state is not permitted, the NOx occlusion amount to the NOx catalyst further increases. However, the subsequent rich operation time is extended, so that the NOx is sufficiently increased. Can be purged. In particular, it is suitable for performing NOx purge even when the NOx occlusion amount is small, that is, when frequently purging NOx.

Furthermore, it is possible to sufficiently perform the subsequent NOx purge by extending the extension time by the amount of time that the rich operation state is not permitted.

Preferred embodiments based on the above solution are as set forth in claims 2 to 8 in the claims. That is,
After switching to the rich operation state, the rich operation state is continued even if acceleration of the vehicle is detected before the purge of the occluded NOx is completed (corresponding to claim 2 ). . In this case, it is preferable to always sufficiently regenerate the NOx catalyst under the condition where the temperature of the NOx catalyst is high without interrupting the purge.

After switching to the rich operation state, the rich operation state is continued even if deceleration of the vehicle is detected before the purge of the storage NOx is completed (corresponding to claim 3 ). . In this case, the same effect as that of the fourth aspect can be obtained.

When the required driving power of the travel motor is larger than the output power of the battery, the rich operation state is prohibited (corresponding to claim 4 ). In this case, it is preferable to sufficiently satisfy the acceleration request for increasing the required driving power of the traveling motor and to secure the acceleration performance.

The lean operation state is performed at a constant load and a constant rotation speed (corresponding to claim 5 ). In this case, the engine is operated in the most efficient state, which is preferable for improving fuel efficiency.

The predetermined time is 10 seconds or longer (corresponding to claim 6 ). In this case, the NOx catalyst (particularly the NOx catalyst used in automobiles) can be reliably heated to the activation temperature or higher, and the subsequent NOx purge can be reliably and efficiently performed.

The engine is operated using hydrogen as fuel (corresponding to claim 7 ). In this case, NOx can be efficiently purged when hydrogen, which tends to have a low exhaust gas temperature, is used as fuel.

When the rich operation state is set, power generation is stopped (corresponding to claim 8 ). In this case, when switching to the rich operation, it is preferable to prevent or reduce the occurrence of pre-ignition and the increase in combustion noise due to the improvement in combustibility due to the rich air-fuel ratio. In particular, when hydrogen is used as fuel while operating the engine at a constant rotation and a constant load, pre-ignition and combustion noise increase are likely to occur in the rich operation state. Even in such a case, pre-ignition generation and combustion noise increase. Can be prevented or reduced.

In order to achieve the above object, the following solution is adopted in the device of the present invention. That is, as described in claim 9 in the claims,
An engine having a NOx catalyst disposed in the exhaust passage;
A generator driven by the engine;
A battery in which the power generated by the generator is stored;
A traveling motor driven by the power generated by the generator and the battery;
A storage amount detecting means for detecting a storage amount of NOx in the NOx catalyst;
When the NOx occlusion amount detected by the occlusion amount detection means is greater than or equal to a predetermined amount, the engine operating state is changed from a lean operation state with an air / fuel ratio leaner than the stoichiometric air / fuel ratio to a rich value that is less than the stoichiometric air / fuel ratio. An air-fuel ratio changing means for switching to a rich operation state at an air-fuel ratio;
The switching to the rich operation state by the air-fuel ratio changing means is performed on the condition that the time during which power generation is performed in the lean operation state is continuously performed for a predetermined time or more when the NOx catalyst becomes the activation temperature or more. Change permission means to allow as,
It is supposed to be equipped with. According to the above solution, an exhaust gas purification device for realizing the exhaust gas purification method corresponding to claim 1 can be provided.

  According to the present invention, it is possible to efficiently purge NOx by confirming that the NOx catalyst has reached the activation temperature without depending on the temperature sensor.

1 is a block diagram illustrating an overall configuration of a vehicle according to an embodiment of the present invention. It is a figure which shows the control system of the vehicle shown in FIG. The time chart which shows the example of control of this invention. The flowchart for performing the example of control of FIG.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a block diagram showing an overall configuration of a vehicle according to an embodiment of the present invention, and FIG. 2 is a diagram showing a control system for the vehicle shown in FIG.

  As shown in FIG. 1, a vehicle 1 according to an embodiment of the present invention is a so-called series hybrid vehicle, and is charged with an engine 10, a generator 20 driven by the engine 10, and electric power generated by the generator 20. The battery 30 has a possible high voltage and large capacity, and a travel motor 40 driven by the power generated by the generator 20 driven by the engine 10 and the discharged power of the battery 30.

  In the vehicle 1, an inverter 50 is provided between the generator 20, the battery 30, and the traveling motor 40, and the generated power of the generator 20 is supplied to the battery 30 and / or the traveling motor 40 via the inverter 50. In addition, the electric power discharged from the battery 30 can be supplied to the traveling motor 40.

  The traveling motor 40 is driven by being supplied with at least one of the generated power of the generator 20 and the discharged power of the battery 30, and the driving force of the traveling motor 40 is supplied to the left and right driving wheels via the differential device 60. This is transmitted to the front wheels 61 and 62, so that the vehicle 1 can travel. The traveling motor 40 can also operate as a generator, and operates as a generator when the vehicle 1 is decelerated, so that the battery 30 can be charged with the generated electric power.

  In the vehicle 1, the engine 10 is used only for power generation in the generator 20. In the present embodiment, the engine 10 is not limited to this, but is stored in the hydrogen fuel tank 70. A hydrogen engine in which gas is supplied as fuel is used.

  As shown in FIG. 2, the engine 10 is a twin-rotor type rotary engine, and includes a rotor 12 that is in contact with the trochoidal surface of the rotor housing 11 at three points to define three working chambers. By rotating, the eccentric shaft 13 as an output shaft is rotated.

  In the engine 10, an intake passage 14 and an exhaust passage 15 are connected to the rotor housing 11, and a hydrogen injector 17 for injecting hydrogen gas when fuel is supplied to the intake passage 14 by a throttle valve 16 and a premixing system. The exhaust passage 15 is provided with an exhaust gas purification catalyst 80 for purifying the exhaust gas. The exhaust gas purification catalyst 80 is a NOx catalyst and stores NOx during the lean operation, while the NOx stored by the rich operation is purged.

  A hydrogen injector 18 and a spark plug 19 for injecting hydrogen gas are also attached to the rotor housing 11 so as to face the working chamber of the rotor housing 11. In FIG. 2, the arrows shown in the intake passage 14 and the exhaust passage 15 indicate the flow of intake or exhaust.

  In addition, the vehicle 1 includes a battery current / voltage sensor (battery remaining capacity detecting means) 101 that detects a current flowing in and out of the battery 30 and a voltage of the battery 30, and an accelerator that detects an amount of depression of an accelerator pedal (accelerator opening). An opening sensor 102, a vehicle speed sensor 103 for detecting the vehicle speed, an engine speed sensor 104 for detecting the speed of the engine 10, and an air-fuel ratio sensor 105 for detecting the air-fuel ratio are mounted. A catalyst temperature detection sensor for detecting the temperature of the exhaust gas purification catalyst 80 is not mounted.

The vehicle 1 is also provided with a control unit 100 that comprehensively controls the configuration related to the vehicle 1. The control unit 100 includes a battery current / voltage sensor 101, an accelerator opening sensor 102, a vehicle speed sensor 103, Various signals are input from the engine speed sensor 104, the air-fuel ratio sensor 105, and the like. The control unit 100 can also output control signals to the inverter 50, the throttle valve actuator 107, the hydrogen injectors 17 and 18, the spark plug 19, and the like.

  The control unit 100 controls the inverter 50 to drive the traveling motor 40 only with the discharge power from the battery 30, the mode with only the generated power from the generator 20, the battery 30 and the fuel tank It is possible to switch between the modes performed with the power from both of the 20.

  The engine 10 controlled by the control unit 100 is normally operated at a lean air-fuel ratio (for example, an excess air ratio λ = 2.3) that is leaner than the stoichiometric air-fuel ratio in order to improve fuel efficiency and improve fuel efficiency. Therefore, the constant rotation speed operation is performed at a constant rotation speed (for example, 2000 rpm) at the most efficient predetermined rotation speed, and the constant load operation is performed.

  When the NOx occlusion amount in the exhaust gas purification catalyst 80, which is a NOx catalyst, increases to a predetermined amount (for example, 50%, which is still sufficient for NOx occlusion), the engine 10 has a stoichiometric air-fuel ratio. Alternatively, the engine is switched to a rich operation state in which the rich air-fuel ratio becomes less than that (for example, λ may be less than 1 in an operation with an excess air ratio λ = 1).

  The rich operation is executed until the NOx occlusion amount in the exhaust gas purification catalyst 80 becomes equal to or lower than a certain lower limit value (for example, 0%) that is sufficiently reduced. In the embodiment, the NOx occlusion amount is reduced to the lower limit value. For a predetermined basic time (for example, 5 seconds corresponding to 50% of NOx occlusion). However, as described later, when switching to the rich operation state is not permitted (when prohibited), the subsequent rich operation time is extended by this disallowed time (for example, 5 seconds of the basic time). On the other hand, the rich operation is performed only for the time when the extension time is added). The engine speed is a constant speed at the same predetermined speed as that during lean operation. Of course, after the NOx occlusion amount in the exhaust gas purification catalyst 80 is sufficiently reduced, the engine 10 is returned to the lean operation again.

  Here, when the rich operation is performed to purge the NOx stored in the exhaust gas purification catalyst 80, the engine 10 is driving the generator 20 (i.e., generating electric power), and the driving load on the engine 10 is increased. May be big. In this case, since hydrogen is used as fuel and efficient constant rotation and constant load operation is performed, there is a very high possibility that pre-ignition will occur or combustion noise will increase.

  In the present embodiment, when the engine 10 is driven by the engine 10 (i.e., when power is being generated), the driving load of the engine 10 is reduced when the engine 10 is switched to the rich operation. The driving load on the engine 10 can be reduced by reducing the generated power while generating power with the generator 20 (for example, 50%). In the embodiment, the generated power is set to zero. It is. The generated power can be adjusted, for example, by adjusting the current supplied to the field winding. If a clutch is provided between the engine 10 and the generator 20, the degree of engagement of the clutch should be adjusted. Can also be performed.

  FIG. 3 is a time chart showing a control example of the present invention. In FIG. 3, at time t0, power generation is performed in the lean operation state, and accordingly, the NOx occlusion amount in the NOx catalyst 80 is gradually increased. At time t1, the NOx occlusion amount has increased to a predetermined value (for example, 50%) at which purging is started. Then, the power generation time in the lean operation state from the time t0 to the time t1 has continued for a predetermined time (for example, 10 seconds) or longer. At this time, at time t1, the operation is immediately switched to the rich operation and purge is executed, and the power generation is stopped and the engine 10 is set to the no-load operation.

  The purge started from time t1 is performed until time t2. The purge time from t1 to t2 is set to the basic time t0 (for example, 5 seconds) corresponding to the NOx occlusion amount in the NOx catalyst 80 being a predetermined value (for example, 50%).

  From time t2 when the purge is completed, power generation is performed again in the lean operation state, and accordingly, the NOx occlusion amount in the NOx catalyst 80 is gradually increased. At time t3, the NOx occlusion amount of the NOx catalyst 80 has reached a predetermined value (for example, 50%). However, at the time point t3, it is a time when the power generation in the lean operation state has been resumed and has not yet continued for a predetermined time from the time point t2. At this time, the purge is started from the time t4 when a predetermined time elapses from the time t2 to the time t3. Then, the purge is finished at time t5. The purge time from t4 to t5 is extended to be longer than the basic time t0 from t1 to t2. The extension time Δt0 is set to be longer as the purge prohibition time (time from the time t3 to the time t4) is longer.

  Once the operation is switched to the rich operation and the purge is started, even if acceleration or deceleration of the vehicle is detected, the basic time t0 (between t1 and t2) or the extended time (between t4 and t5) ) Is continued until the rich operation state is continued, the NOx catalyst is sufficiently regenerated, the NOx occlusion amount becomes the lower limit (for example, 0%), and the subsequent estimation accuracy of the NOx occlusion amount is ensured. It can be so.

  FIG. 4 shows a flowchart for performing the control as shown in FIG. Hereinafter, this flowchart will be described. In the following description, Q indicates a step. First, in Q1, signals from various sensors are read. Thereafter, at Q2, it is determined whether or not the engine 10 is in a condition for power generation operation. In other words, the power generation operation of the engine 10 is stopped when the charge amount (remaining capacity) of the battery 30 is a predetermined value (for example, 80%) or more, and the power generation operation is performed otherwise.

  If NO in Q2, the process returns to Q1. When the determination in Q2 is YES, in Q3, power generation is performed while the engine 10 is in a lean operation. After Q3, in Q4, it is determined whether or not the NOx occlusion amount in the NOx catalyst 80 is equal to or greater than a predetermined value (for example, 50%) set in advance. Note that the calculation of the NOx occlusion amount can be estimated based on, for example, the lean operation time from the start of the lean operation, and other appropriate methods can be adopted.

  If NO in Q4, the process returns to Q1. If YES in Q4, it is determined in Q5 whether power generation in the lean operation has been continuously performed for a predetermined time (for example, 10 seconds) until the time point in which Q4 is determined to be YES. . The predetermined time is set as a time necessary and sufficient for the NOx catalyst 80 to be heated to the activation temperature or higher.

  If YES in Q5, it is determined in Q6 whether or not the required drive power of the traveling motor 40 is greater than the output power of the battery 30. When the determination in Q6 is NO, the output power of the battery 30 has a margin. In this case, in Q7, the rich operation is started and the power generation is set to 0 (no load purge). By starting the rich operation, NOx stored in the NOx catalyst 80 is purged. In addition, since the engine 10 is substantially in a no-load operation due to the stoppage of power generation, the generation of pre-ignition and the increase in combustion noise due to the rich operation are prevented or reduced.

  After Q7, at Q8, it is determined whether or not a predetermined time tp has elapsed since the start of the rich operation. The predetermined time tp is a time obtained by adding an extension time Δt0 described later to a basic time t0 (for example, 5 seconds) corresponding to 50% of the NOx occlusion amount in the NOx catalyst 80. If the determination in Q8 is NO, the process returns to Q7. That is, once the operation is switched to the rich operation and the purge is started, the rich operation state is continued until the predetermined time tp elapses even if the acceleration or deceleration of the vehicle is detected. When the determination in Q8 is YES, purging is completed, and in Q9, the no-load operation at the rich air-fuel ratio is stopped, and the state returns to the state where power generation is performed in the lean operation. In Q9, the NOx estimated storage amount of the NOx catalyst 80 is reset to zero.

  When NO is determined in Q5 or YES in Q6, the process returns to Q1 after the process of Q10. The transition to Q10 is when the storage NOx purge is not permitted (when prohibited). At this time, the extension time Δt0 is set by an amount corresponding to the increase in the storage NOx in the NOx catalyst 80 from the time point when the determination in Q4 is YES. That is, the subsequent rich operation time tp is a time obtained by adding the extension time Δt0 to the basic time t0. Of course, as the increased NOx occlusion amount increases, the extension time Δt0 is set longer, but an upper limit (for example, 5 seconds) can be provided for the extension time. By the process of Q10, the subsequent purge time is extended by the time for which the NOx purge is prohibited, and the NOx catalyst 80 is always sufficiently regenerated by one purge.

  Although the embodiment has been described above, the present invention is not limited to the embodiment, and can be appropriately changed within the scope described in the scope of claims. For example, the invention includes the following cases. . The engine 10 may be a reciprocating engine, or may be an engine using a fuel other than hydrogen as the fuel. The driving load of the engine 10 during the purge execution may be reduced by reducing the generated power to, for example, 20 to 50%, although the power generation is performed instead of setting the generated power of the generator 20 to zero. Of course, the object of the present invention is not limited to what is explicitly stated, but also implicitly includes providing what is substantially preferred or expressed as an advantage.

  The present invention is suitable for exhaust gas purification using a NOx catalyst.

10: Engine 15: Exhaust passages 17, 18: Fuel injection valve 19: Spark plug 20: Generator 30: Battery 40: Driving motor 70: Hydrogen tank 80: Exhaust gas purification catalyst (NOx catalyst)
100: Control unit (control means)

Claims (9)

An engine in which an NOx catalyst is disposed in the exhaust passage, a generator driven by the engine, a battery storing electric power generated by the generator, a driving motor driven by the electric power generated by the generator, and the battery; An exhaust gas purification method for an internal combustion engine comprising:
A first step of detecting a storage amount of NOx in the NOx catalyst;
When the NOx occlusion amount detected in the first step is greater than or equal to a predetermined amount, the engine operating state is changed from a lean operating state at an air / fuel ratio leaner than the stoichiometric air / fuel ratio to a rich air / fuel ratio below the stoichiometric air / fuel ratio. A second step of switching to a rich operation state at a fuel ratio;
With
The switching to the rich operation state continues for a predetermined time or more set as a time sufficient for the temperature of the power generation in the lean operation state to be raised until the NOx catalyst reaches the activation temperature or higher. Allowed on the condition that
When the NOx occlusion amount detected in the first step is equal to or greater than the predetermined amount, when switching to the rich operation state is not permitted, the operation time in the rich operation state performed thereafter is extended,
The operation time in the rich operation state is an addition time obtained by adding the extension time to the basic time that is the minimum operation time,
The extended time is increased as the time during which switching to the rich operation state is not permitted is longer,
An exhaust gas purification method for an internal combustion engine. Oite to claim 1,
The exhaust gas of the internal combustion engine, wherein the rich operation state is continued even after acceleration of the vehicle is detected after the switching to the rich operation state until the purge of the storage NOx is completed Purification method. In claim 1 or claim 2 ,
The exhaust gas of the internal combustion engine, wherein the rich operation state is continued even after the deceleration of the vehicle is detected after the storage NOx purge is completed after the change to the rich operation state Purification method. In any one of Claims 1 thru | or 3 ,
An exhaust gas purification method for an internal combustion engine, characterized in that the rich operation state is prohibited when the required driving power of the travel motor is larger than the output power of the battery. In any one of Claims 1 thru | or 4 ,
The exhaust gas purification method for an internal combustion engine, wherein the lean operation state is performed at a constant load and a constant rotation speed. In any one of Claims 1 thru | or 5 ,
The exhaust gas purification method for an internal combustion engine, wherein the predetermined time is 10 seconds or more. In any one of Claims 1 thru | or 6 ,
An exhaust gas purification method for an internal combustion engine, wherein the engine is operated using hydrogen as a fuel. In any one of Claims 1 thru | or 7 ,
The exhaust gas purification method for an internal combustion engine, wherein power generation is stopped when the rich operation state is set. An engine having a NOx catalyst disposed in the exhaust passage;
A generator driven by the engine;
A battery in which the power generated by the generator is stored;
A traveling motor driven by the power generated by the generator and the battery;
A storage amount detecting means for detecting a storage amount of NOx in the NOx catalyst;
When the NOx occlusion amount detected by the occlusion amount detection means is greater than or equal to a predetermined amount, the engine operating state is changed from a lean operation state with an air / fuel ratio leaner than the stoichiometric air / fuel ratio to a rich value that is less than the stoichiometric air / fuel ratio. An air-fuel ratio changing means for switching to a rich operation state at an air-fuel ratio;
The switching to the rich operation state by the air-fuel ratio changing means is set as a time necessary and sufficient for the time during which power generation is performed in the lean operation state until the NOx catalyst reaches the activation temperature or higher. Change permission means for permitting on condition that it is continuously performed for a predetermined time or more,
When the NOx occlusion amount detected by the occlusion amount detection means is equal to or greater than the predetermined amount, when switching to the rich operation state is not permitted, an extension of the operation time in the rich operation state performed thereafter is Extended time setting means for setting so as to increase as the time during which switching to the rich operation state is not permitted,
With
The operation time in the rich operation state is an addition time obtained by adding the extension time set by the extension time setting means to the basic time that is the minimum operation time.
An exhaust gas purification apparatus for an internal combustion engine, characterized in that:

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